This study aimed to give insights of in-service teachers' experiences of nature of science (NOS) learning and NOS teaching through a co-teaching professional learning context. For this purpose, the co-teachers were encouraged to share and discuss ideas and to improve NOS teaching through reflection and collaborative interaction in the context of a Saturday science teaching program. The program provided students in Grades K-2 with hands-on activities covering various science topics over 5 weekly 2.5-h sessions. One co-teacher was an experienced university teacher; the other was an experienced primary teacher without NOS teaching experience. Data were collected by use of pre- and post-instruction of the Views of Nature of Science questionnaire, follow-up interviews, written artifacts, and videotaped teaching sessions. Results showed that co-teaching contributed to the teacher's NOS learning as well as NOS teaching. The teacher recognized subjective, creative, empirical, and sociocultural NOS; she started to use NOS vocabulary more comfortably and developed teaching strategies and examples for sociocultural NOS.